It is known to provide molded plastic taps for use with containers, in particular disposable containers of the type popular for supplying liquid such as water, wine or milk. One well known type of tap for this purpose is a so-called push button tap having a resilient plastic diaphragm which, when pressed, opens the valve to allow liquid to flow from the container. The resilient plastic diaphragm, commonly referred to as a “push button,” can be arranged so that it positively urges the valve into a sealing position when manual pressure is removed therefrom. The tap is therefore self-closing.
An alternative to push button taps are the so-called “rotary” taps. In these, a cap is rotated to in turn rotate a stem within the tap body. Rotation of the stem causes it to uncover an aperture provided in the tap body through which or from which liquid is dispensed.
Irrespective of the type of tap used with a container, it has been found that smooth liquid flow with a stabilized flow profile can only be achieved if either the container is flexible, collapsing as liquid is dispensed, or the container is vented. The reason for this is that otherwise air must flow into the container to fill the space from which liquid has been vacated and equalize the pressure within the container. The inflow of air disrupts the outflow of liquid causing it to be uneven and reducing the flow rate.